1. Field of the Invention
The present invention relates to a dielectric resonator. More specifically, the present invention relates to a structure for adjusting a resonant frequency of the dielectric resonator utilizing the TE.sub.01.delta. mode or the modified mode thereof.
2. Description of the Prior Art
One example of the prior art is disclosed, for example, in Japanese Utility Model Laid Open No. 122909/1982. In this prior art document, the resonant frequency is disclosed to be adjusted in such a way that, a dielectric resonant element is retained within a metal case and a dielectric resonator utilizing the TE.sub.01.delta. mode is realized. On the metal case, a metal screw is mounted so as to be brought close to or away from the dielectric resonator element by moving the screw up and down in adjusting the resonant frequency. For example, when the metal screw approaches the dielectric resonator element, the resonant frequency becomes higher.
In the prior art device using the metal screw, the adjustable range of the resonant frequency is narrow. For example, if the resonant frequency is fo and its variation is .DELTA.fo, the ratio .DELTA.fo/fo is found to be below 0.2% (.DELTA.fo/fo.ltoreq.0.2%). This is because that, if the variation .DELTA.fo increases, the unloaded Q (Qo) deteriorates considerably and the ratio becomes .DELTA.Qo/Qo.gtoreq.10%, which is not practical for use.